1. Field of the Invention
This invention relates to a gauge to measure a coating thickness with at least one probe, that has at least one sensor as well as a device to make the zero adjustment and/or the calibration.
2. Description of the Related Art
All gauges on the market to measure a coating thickness require a regular check of the zero adjustment and, if necessary, of the calibration. This has several reasons. Either the gauges were out of use for a longer period of time, batteries had to be exchanged, or measuring conditions considerably vary from normal conditions due to extreme environmental temperature fluctuation, changes to kind or thickness of substrate, the gauge or the probe themselves. As a rule, even the exchange of the probe requires a new zero adjustment or calibration. To do so, prior to taking a measurement the gauges or the probes have to be placed on a reference plate and the zero adjustment or calibration has to be started by pressing the operation button. This procedure is, for example, described in patent DE 34 04 720.
U.S. Pat. No. 5,293,132 also states a method for zero adjustment, where the user has to decide on which substrate a measurement will be taken in order to, if necessary, manually switch the gauge in case of a change of material. In case of a material change the user is requested by the device to make a zero adjustment. The user is compelled by the described device to do the zero adjustment, as otherwise no measurement can be taken. With other known devices there is the danger that with omitted adjustment of the device the measuring results are falsified. By no means, the device has integrated reference plates so that via control elements the device has to be informed about the type of reference plate in use during manual adjusting. This may cause confusion.
A further disadvantage of the previous gauges is that the zero adjustment and positioning depends on how it is performed. The placing of the probe at different spots or uneasy placing may possibly cause very different results. This does not only lead to inaccuracy but also makes it difficult to compare measuring results of measuring gauges that usually have comparable characteristics.
Furthermore, devices to measure a coating thickness with separate probes are known, that are either connected with the device via a cable or data are wirelessly transferred to the measuring gauge. The probes are designed in a way that the taking of measurements starts upon placing them on the surface to be tested. But control elements are still necessary to do the zero adjustment or calibration. The adjustment or calibration on reference plates has to be started and realized individually by the user.
It is the task of the invention in question to propose a coating thickness measuring device that avoids the usual difficulties and error sources that are resulting from zero adjustment and calibration necessary for the known measuring gauges.
This task is solved by the device in accordance with the invention by providing the coating thickness measuring device with means that in case of interaction, especially in case of contact or a relative movement between a sensor and a reference plate, automatically activate the zero adjustment or calibration. Especially, the advantage of this device is that the user of the device always gets a correct adjustment made under the same conditions. Thus the adjustment is not subjected to individual influences.
Preferred versions of the invention are defined by the sub-claims.
For example, a device with a removable probe unit in accordance with a preferred version is proposed, that upon having been taken out automatically performs the zero-adjustment thus the measurement can be taken immediately.
Moreover, the coating thickness measuring device in accordance with the invention can have integrated reference plates. Advantageously, when placing the probe the device recognizes on which reference plate the zero-adjustment or calibration shall be made and automatically carries it out without control elements being actuated by the user.